Method and apparatus for allocating radio resource using random access procedure in a mobile communication system

ABSTRACT

Disclosed is a method for performing a random access in a wireless communication, including identifying a channel condition and a size of a message that a user equipment will transmit after a transmission of a preamble, selecting a first preamble set from at least two preamble sets if the channel condition is greater than a first threshold and the size of the message is greater than a second threshold, selecting a preamble from the selected first preamble set if the first preamble set is selected, transmitting, to a base station, the selected preamble, receiving, from the base station, a random access response message including resource allocation information in response to the transmission of the selected preamble, and transmitting, to the base station, the message based on the resource allocation information.

PRIORITY

This application is a Continuation Application of U.S. application Ser.No. 14/863,668, filed in the U.S. Patent and Trademark Office on Sep.24, 2015, which is a continuation of U.S. application Ser. No.13/903,631, filed in the U.S. Patent and Trademark Office on May 28,2013, now U.S. Pat. No. 9,374,836, issued on Jun. 21, 2016, which is acontinuation of U.S. application Ser. No. 11/924,368, filed in the U.S.Patent and Trademark Office on Oct. 25, 2007, now U.S. Pat. No.8,451,781, issued on May 28, 2013, and claims priority under 35 U.S.C.§119(a) to a Korean Patent Application filed in the Korean IntellectualProperty Office on Oct. 25, 2006 and assigned Serial No.10-2006-0103809, the contents of each of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to a mobile communicationsystem, and in particular, to a method and apparatus for efficientlyallocating radio resources to transmit an uplink message of a terminal,or User Equipment (UE), by a network node.

2. Description of the Related Art

The Universal Mobile Telecommunication Service (UMTS) system is a 3rdGeneration (3G) asynchronous mobile communication system employingWideband Code Division Multiple Access (WCDMA) based on Global Systemfor Mobile Communications (GSM) and General Packet Radio Services(GPRS), both of which are European mobile communication systems. In 3rdGeneration Partnership Project (3GPP) in charge of UMTS standardization,a Long Term Evolution (LTE) system is under discussion as the nextgeneration mobile communication system of the UMTS system. The presentinvention will be described herein with reference to the LTE system,which will now be briefly described.

LTE is a technology for implementing packet-based communication at ahigh data rate of a maximum of about 100 Mbps, aiming atcommercialization in around 2010. To this end, several schemes are underdiscussion, such as one for reducing the number of nodes located in acommunication path by simplifying a configuration of the network, andanother for maximally approximating radio protocols to radio channels.

FIG. 1 illustrates an Evolved UMTS mobile communication system to whichthe present invention is applied.

Referring to FIG. 1, an Evolved UMTS Radio Access Network (E-UTRAN orE-RAN) 110 is simplified to a 2-node configuration of Evolved Node Bs(ENBs) 120, 122, 124, 126 and 128, and anchor nodes 130 and 132. A UE101, or terminal, accesses an Internet Protocol (IP) network by means ofthe E-UTRAN 110.

The ENBs 120 to 128 correspond to the existing Node B of the UMTSsystem, and are connected to the UE 101 over radio channels. Compared tothe existing Node B, the ENBs 120 to 128 perform more complex functions.Particularly, in LTE, because all user traffic including the real-timeservices, such as Voice over IP (VoIP), is serviced over a sharedchannel, the ENB collects status information of UEs to performscheduling depending thereon, and controls a function related tomanagement of radio resources. In addition, control protocols, such asRadio Resource Control (RRC), are included in the ENBs 120 to 128.Generally, each ENB controls a plurality of cells.

To realize the data rate of a maximum of 100 Mbps, LTE uses OrthogonalFrequency Division Multiplexing (OFDM) as a radio access technology in a20-MHz bandwidth. Further, the ENB performs Adaptive Modulation & Coding(AMC) that adaptively determines a modulation scheme and a channelcoding rate according to channel status of the UE 101.

Like the mobile communication system supporting High Speed DownlinkPacket Access (HSDPA), High Speed Uplink Packet Access (HSUPA), andEnhanced Dedicated Channel (E-DCH) services, the LTE system alsoperforms Hybrid Automatic Repeat reQuest (HARQ) between the UE 101 andthe ENBs 120 to 128. Because various Quality of Service (QoS)requirements cannot be satisfied only with HARQ, Outer ARQ in the upperlayer can be performed between the UE 101 and the ENBs 120 to 128.

The HARQ is a technique for soft-combining previously received data withretransmitted data without discarding the previously received data,thereby increasing the reception success rate. This is used to increasethe transmission efficiency in high-speed communication such as HSDPAand EDCH.

The random access procedure to which the present invention is applied isused as a procedure between a UE and a network node, in which a UE inRRC idle mode or an RRC connected mode matches uplink timing sync withthe ENB for (initial) uplink message/data transmission, sets initialuplink transmission power, and/or requests radio resource allocation forthe (initial) uplink message/data transmission. For a definition of theRRC idle mode and RRC connected mode, reference can be made to the 3GPPTR25.813v700 standard.

In brief, the RRC idle mode generally refers to a state of a UE, inwhich the ENB has no context information for the UE and the anchor node,or upper node, has context information of the UE, so a location of theUE is managed not in units of cells but in units of tracking area forpaging.

The RRC connected mode refers to a state of a UE, in which not only theanchor node but also the ENB have the context information of the UE andan RRC connection is set up between the UE and the ENB, so the locationof the UE can be managed in units of cells.

FIG. 2 illustrates a conventional random access procedure in a 3GPP LTEsystem.

Referring to FIG. 2, reference numeral 210 denotes a UE, and referencenumeral 211 denotes an ENB that controls the cell in which the UE 210 islocated.

Step 221 indicates an operation in which the UE 210 triggers a randomaccess procedure. For example, this can indicate the case where to starta call, an RRC idle mode UE (UE in the RRC idle mode) needs to transmitan uplink control message which allows the ENB 211 to acquire UE contextinformation, set up an RRC connection between the UE 210 and the ENB211, and transmit a service request to an anchor node.

If the random access procedure is triggered in step 221, the UE 210randomly selects one of a total of X random access preambles agreed withthe ENB 211 in step 231. Thereafter, in step 241, the UE 210 transmitsthe selected random access preamble to the ENB 211 over a predeterminedchannel/time.

When transmitting the random access preamble in step 241, the UE 210sets initial random access preamble's transmission power of UE byapplying Open Loop Power Control (OLPC). Equation (1) shows theconventional manner of performing the conventional OLPC.

PTX=L _(pilot) I _(BTS) SIR _(TARGET)  (1)

The parameters of Equation (1) are defined as follows:

-   -   P_(TX): a transmission power level [dBm] of a channel DPCH;    -   L_(pilot): a path loss [dB] estimated using a measure of a        downlink pilot channel and a transmission power of a signaled        pilot channel;    -   I_(BTS): an interference level that a receiver of an ENB (or        Base Transceiver System (BTS)) experiences;    -   SIR_(TARGET): a target Signal-to-Interference Ratio (SIR) [dB]        for maintaining the transmission quality of each UE. It can be        either signaled separately for each UE or signaled commonly for        all UEs.

If the random access preamble is retransmitted due to the failure in theinitial random access preamble transmission of step 241, a delta value(hereinafter power ramp step) is added to the power that is set duringthe previous random access preamble transmission. The power ramp stepcan be either signaled, or defined as a specific value.

In step 242, the ENB 211 transmits to the UE 210 a response message tothe random access preamble received in step 241. The response message242 includes such information as a random access preamble identifierindicating the random access preamble received in step 231, uplinktiming sync information for matching uplink timing sync and radioresource allocation information for transmission 251 of the next uplinkupper message of the UE 210.

In the transmission of the response message by the ENB 211 in step 242,the ENB 211 can perform synchronous transmission using the timingrelationship determined for the transmission of step 241 by the UE 210.

If the information received in step 242 includes a random accesspreamble IDentifier (ID) mapped to the random access preambletransmitted in step 241 by the UE 210 itself, the UE 210 corrects theuplink transmission timing, using the uplink timing sync informationincluded in the received information of step 242. In step 251, the UE210 transmits the corresponding upper message over the correspondingchannel/time using the allocated radio resources.

The message transmitted in step 251 can be an RRC message or aNon-Access Stratum (NAS) message. Alternative, the message can be acombined message of the RRC message and the NAS message. Here, the RRCmessage indicates a message for Radio Resource Control (RRC), having aUE and an ENB as protocol endpoints, and the NAS message indicates amessage for controlling parameters such as mobility, service and sessionof a UE, having a UE and an anchor node as protocol endpoints.

However, in the 3GPP LTE system that performs the random accessprocedure of FIG. 2, when the ENB 211 allocates, to the UE 210, radioresources for transmission of an upper message in step 242, it canperform resource allocation only for the message size guaranteed suchthat all UEs in the cell can transmit the message. This is because whenthe ENB 211 receives the random access preamble from the UE 210 in step241, the information transmitted through the random access preamble onlyincludes a random ID.

In other words, the random access preambles have only the random IDswithout including other information, to prevent the UE 210 fromselecting the same random access preamble, thus preventing occurrence ofthe collision.

Therefore, because the ENB 211, receiving this random access preamble,cannot acquire any information necessary for scheduling, from the randomaccess preamble, even though the UE is located in the cell boundary, theENB 211 cannot allocate the radio resources for thetransmission-guaranteed message size.

Therefore, the random access procedure of the mobile communicationsystem shown in FIG. 2 is inefficient in scheduling the next messagetransmitted from the UE 210 by the ENB 211.

In addition, if the ENB 211 includes in the random access preambles theinformation (e.g., cause/type information of the random accessprocedure, priority information of the random access procedure and radiochannel condition information) capable of assisting in performingscheduling, the ENB 211 may very efficiently perform scheduling on thenext message transmitted from the UE 210.

However, the number of random access preambles that the UE can guaranteethe transmission at any place in the cell is limited, using the limitedradio resources when there is no RRC connection set up between the UEand the ENB.

To carry all the information on the limited random access preamblesdecreases the number of random IDs that reduce the collisionprobability, thereby causing the increasing collision problem thatmultiple UEs select the same random access preamble in the random accessprocedure, in which procedure an increase in the collision probabilityto at least a certain level may raise a fatal problem.

Therefore, the current mobile communication system needs an efficientrandom access procedure for solving the foregoing problems.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least the problemsand/or disadvantages and to provide at least the advantages describedbelow. Accordingly, an aspect of the present invention is to provide amethod and apparatus capable of efficiently allocating radio resourcesto transmit an uplink message of a UE by a network node after receivinga random access preamble, based on efficient random access preambledesign in a random access procedure.

Another aspect of the present invention is to provide a method andapparatus in which a UE transmits an efficient random access preamble toa network node and receives radio resources allocated therefrom, basedon efficient random access preamble design in the mobile communicationsystem.

According to the present invention, there is provided a method forperforming a random access in a wireless communication, includingidentifying a channel condition and a size of a message that a userequipment will transmit after a transmission of a preamble, selecting afirst preamble set from at least two preamble sets if the channelcondition is greater than a first threshold and the size of the messageis greater than a second threshold, selecting a preamble from theselected first preamble set if the first preamble set is selected,transmitting, to a base station, the selected preamble, receiving, fromthe base station, a random access response (RAR) message includingresource allocation information in response to the transmission of theselected preamble, and transmitting, to the base station, the messagebased on the resource allocation information.

According to the present invention, there is provided an apparatus forperforming a random access in a wireless communication, including atransceiver configured to transmit or receive data, and a controllerconfigured to identify a channel condition and a size of a message thata user equipment will transmit after a transmission of a preamble,select a first preamble set from at least two preamble sets if thechannel condition is greater than a first threshold and the size of themessage is greater than a second threshold, select a preamble from theselected first preamble set if the first preamble set is selected,transmit, to a base station, the selected preamble, receive, from thebase station, an RAR message including resource allocation informationin response to the transmission of the selected preamble, and transmit,to the base station, the message based on the resource allocationinformation.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 illustrates a configuration of a 3GPP LTE system to which thepresent invention is applied;

FIG. 2 illustrates a conventional random access procedure in the 3GPPLTE system;

FIG. 3 illustrates a random access procedure obtained based on therandom access preamble design according to the present invention;

FIG. 4 illustrates a UE's operation based on the random access preambledesign according to the present invention;

FIG. 5 illustrates an ENB's operation based on the random accesspreamble design according to the present invention;

FIG. 6 illustrates a block diagram of a UE's apparatus according to thepresent invention; and

FIG. 7 illustrates a block diagram of an ENB's apparatus according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the annexed drawings. In the followingdescription, a detailed description of known functions andconfigurations incorporated herein has been omitted for the sake ofclarity and conciseness.

Although the present invention will be described herein with referenceto a Long Term Evolution (3GPP LTE) system evolved from the 3rdGeneration Partnership Project (3GPP) Universal Mobile TelecommunicationService (UMTS) system, by way of example, the present invention can beapplied to all mobile communication systems to which ENB scheduling isapplied, without separate modification.

In addition, the present invention can be applied to the communicationsystems to which the random access procedure is applied, withoutseparate modification. Further, the present invention can be applied tothe systems supporting uplink services.

The present invention provides a scheme in which a network node canefficiently allocate radio resources to transmit an uplink message froma UE upon receipt of a random access preamble through efficient randomaccess preamble design in a random access procedure.

Therefore, when a UE is in a good radio channel condition and a size ofa message that the UE will transmit after transmitting a random accesspreamble and receiving a response thereto is greater than a predefinedminimum message size, the present invention separately defines a randomaccess preamble set that the UE will select in the random accessprocedure. In another case, i.e. when the radio channel condition of theUE is not good or the size of the message that the UE will transmitafter transmitting a random access preamble and receiving a responsethereto is less than or equal to the predefined minimum message size,the present invention separately defines a random access preamble setthat the UE will select in the random access procedure.

In addition, when the UE is in the good radio channel condition and thesize of the transmission message is greater than the predefined minimummessage size, the UE provides the information to the network node withuse of the corresponding random access preamble set, so the network nodecan allocate radio resources so that it can transmit a message greaterthan the predefined minimum message size over a response message to therandom access preamble.

Further, when the radio channel condition of the UE is not good or thesize of the message that the UE will transmit after transmitting therandom access preamble and receiving a response thereto is less than orequal to the predefined minimum message size, the UE provides theinformation to the network node with use of the random access preambleset corresponding thereto, so the network node can allocate radioresources so that it can transmit a message corresponding only to thepredefined minimum message size over a response message to the randomaccess preamble.

Therefore, the present invention provides a scheme for allowing an ENBto efficiently perform scheduling on the next message sent from a UE byincluding the minimum supplemental information in the random accesspreamble design.

According to the present invention, the supplemental informationindicates an occasion when a UE is in a radio channel condition that isgreater than a threshold Y and a size of the message that the UE willtransmit next is greater than a transmission-guaranteed minimum messagesize Z even though the UE is located in the cell boundary.

That is, a total of X random access preambles agreed between the UE andthe ENB are divided into two sets. One arbitrary set A is defined toindicate an occasion when the UE is in a radio channel condition that isgreater than the threshold Y and a size of the next message that the UEwill transmit is greater than the minimum message size Z. Another set Bis defined to be used when the above condition is unsatisfied.

As a result, upon receipt of a random access preamble corresponding tothe set A, the ENB can allocate radio resources for transmission of amessage greater than Z when scheduling transmission of the next messageof the UE. However, upon receipt of a random access preamblecorresponding to the set B, the ENB can allocate radio resources fortransmission of a message with the size Z when scheduling transmissionof the next message of the UE.

The threshold Y used for determining a good radio channel condition orthe size Z of a message, transmission of which is guaranteed even in thecell boundary, can be either determined as one value regardless the celland undergo hard-coding, or signaled through broadcasted systeminformation according to cells.

It is noted that throughout the description herein, a radio channelcondition that is determined to be greater than a threshold, indicatesthat the radio channel condition is better than a condition related tothe particular threshold.

Table 1 shows an example of the random access preamble design disclosedin the present invention when the total number of random accesspreambles is assumed to be X=64. Although the set A and the set B areequal in the number X/2 of allocated random access preambles in Table 1,by way of example, the set A and the set B may be different in thenumber of random access preambles allocated thereto.

TABLE 1 Set Random ID Random access preamble # Set A 0 Random accesspreamble #0 1 Random access preamble #1 2 Random access preamble #2 3Random access preamble #3 4 Random access preamble #4 5 Random accesspreamble #5 6 Random access preamble #6 7 Random access preamble #7 8Random access preamble #8 9 Random access preamble #9 10 Random accesspreamble #10 11 Random access preamble #11 12 Random access preamble #1213 Random access preamble #13 14 Random access preamble #14 15 Randomaccess preamble #15 16 Random access preamble #16 17 Random accesspreamble #17 18 Random access preamble #18 19 Random access preamble #1920 Random access preamble #20 21 Random access preamble #21 22 Randomaccess preamble #22 23 Random access preamble #23 24 Random accesspreamble #24 25 Random access preamble #25 26 Random access preamble #2627 Random access preamble #27 28 Random access preamble #28 29 Randomaccess preamble #29 30 Random access preamble #30 31 Random accesspreamble #31 Set B 0 Random access preamble #32 1 Random access preamble#33 2 Random access preamble #34 3 Random access preamble #35 4 Randomaccess preamble #36 5 Random access preamble #37 6 Random accesspreamble #38 7 Random access preamble #39 8 Random access preamble #40 9Random access preamble #41 10 Random access preamble #42 11 Randomaccess preamble #43 12 Random access preamble #44 13 Random accesspreamble #45 14 Random access preamble #46 15 Random access preamble #4716 Random access preamble #48 17 Random access preamble #49 18 Randomaccess preamble #50 19 Random access preamble #51 20 Random accesspreamble #52 21 Random access preamble #53 22 Random access preamble #5423 Random access preamble #55 24 Random access preamble #56 25 Randomaccess preamble #57 26 Random access preamble #58 27 Random accesspreamble #59 28 Random access preamble #60 29 Random access preamble #6130 Random access preamble #62 31 Random access preamble #63

Although not shown herein, the present invention can be extended asfollows. For example, if other 2-bit information except for a random IDcan be included in a random access preamble, the random access preamblecan be designed as the following Sets A-D.

-   -   Random Access Preamble Set A: This set is used when a radio        channel condition is determined to be greater than a than a        threshold Y1 and a size of the message that the UE will transmit        next is greater than a minimum size Z1 of a message        transmittable even in the cell boundary, and less than or equal        to a particular size Z2.    -   Random Access Preamble Set B: This set is used when a radio        channel condition is determined to be greater than a threshold        Y2 and a size of the message that the UE will transmit next is        greater than the particular size Z2 limited to the random access        preamble set #A, and less than or equal to a particular size Z3.    -   Random Access Preamble Set C: This set is used when a radio        channel condition is determined to be greater than a threshold        Y3 and a size of the message that the UE will transmit next is        greater than a particular size Z3 limited to the random access        preamble set #B, and less than or equal to a particular size Z4.    -   Random Access Preamble Set #D: This set is used when a radio        channel condition is determined to be greater than a threshold        Y4 and a size of the message that the UE will transmit next is        greater than a particular size Z4 limited to the random access        preamble set #B.

FIG. 3 illustrates an example of a random access procedure obtainedbased on the random access preamble design disclosed in the presentinvention. Reference numeral 310 denotes a UE, and reference numeral 311denotes an ENB that controls and manages the cell in which the UE 310 islocated.

Referring to FIG. 3, step 321 indicates an operation in which the UE 310triggers the random access procedure. For example, this can indicate thecase where to start a call, an RRC idle mode UE needs to transmit anuplink control message.

Step 323 indicates an operation in which random access procedure-relatedcontrol parameters are broadcasted as system information in the cell.The random access procedure-related parameters can include suchinformation as radio resource allocation information used for performingthe random access procedure and radio channel condition threshold Y,transmission power.

The radio resource allocation information used for the random accessprocedure indicates time/frequency radio resources with which the UE 310will transmit a random access preamble in the random access procedure.The radio channel condition threshold Y is a criterion used when the UE310 determines in step 331 whether it is in a good radio channelcondition. The transmission power is a value used when the UE 310determines the radio channel condition.

In particular, the transmission power is a value used when calculating apath loss in the radio channel condition, and the path loss can becalculated using Equation (2), as follows.

Path Loss=Transmission Power−Reception Power  (2)

Herein, the path loss is a value acquired in a long term determined bysuch parameters as propagation loss, shadowing, slow fading and antennapattern, and because the downlink and uplink show the similar values,the path loss information can be used for estimating the uplink channelstatus.

Although it is shown in FIG. 3 that step 323 is performed after step321, if the UE 310 has already acquired the latest random accessprocedure-related parameter through the previous system informationbefore the random access procedure is triggered in step 321, the UE 310can perform the next step 331 immediately after the random accessprocedure is triggered in step 321, since the system informationincluding the random access procedure-related parameter is periodicallytransmitted in the cell. Thus, if the UE 310 has already acquired thelatest random access procedure-related parameter before step 321, thereception of the system information in step 323 can be omitted.

Upon receiving the random access procedure-related parameter through thesystem information in step 331, the UE 310 determines based on theparameter whether it is in a radio channel condition that is greaterthan a threshold Y and a size of the message that the UE 310 willtransmit is greater than a minimum message size Ztransmission-guaranteed in the cell boundary.

The radio channel condition can be determined by two separate methods.In a first method, the UE uses Channel Quality Information (CQI)indicating a received Signal-to-Noise Ratio (SNR) obtained by measuringa downlink pilot. In a second method, the UE 310 uses the path lossinformation defined in Equation (2) rather than the channel qualityinformation.

Herein, the channel quality information indicates a value obtained byconsidering fast fading, and because the fast fading occursindependently in the downlink and the uplink, the channel qualityinformation may not be suitable to be used for estimating the uplinkchannel status and performing scheduling for transmission of the initialuplink message. Therefore, the path loss information is used instead ofthe channel quality information. Generally, because the path loss issimilar to some extent in both the downlink and the uplink, the pathloss, compared to the channel quality information, may be suitable forestimating the uplink channel status and performing scheduling fortransmission of the initial uplink message. That is, the channel qualityinformation and the path loss are interchangeable as parameters than canbe used for estimating the uplink channel status, and can be selectedbased on the circumstances or the system designer's choice.

Although the present invention uses a method of comparing the path lossinformation with a threshold Y, by way of example, the present inventiondoes not exclude a method of comparing the channel quality informationwith a threshold Y.

Therefore, in step 331, the UE 310 determines a path loss in accordancewith Equation (2) using the transmission power received in step 323 andthe reception power for a downlink pilot channel measured for a setinterval. Thereafter, the UE 310 compares the acquired path loss withthe radio channel condition threshold Y received in step 323. If thepath loss is less than or equal to the threshold Y, it is determinedthat the UE 310 is in a radio channel condition that is greater than thethreshold Y. This is because the path loss has an inverse proportionalrelationship with the decision on whether the UE 310 is in the goodradio channel condition.

However, if the channel quality information is used according to thesecond method, the channel quality information has a proportionalrelationship between with the decision on whether the UE 310 is in thegood radio channel condition. Accordingly, the UE 310 determines in step331 a received SNR for the downlink pilot channel measured for aninterval. Thereafter, the UE 310 compares it with the radio channelcondition threshold Y received in step 323. If the channel qualityinformation is greater than or equal to the threshold Y, the UE 310determines that it is in the radio channel condition that is greaterthan the threshold Y.

Further, in step 331, the UE 310 determines whether a size of thetransmission message is greater than the minimum message size Ztransmission-guaranteed in the cell boundary. As to the minimum messagesize Z checked herein, the minimum message size can be set to onestandard value, or a different value can be signaled for every cellthrough the system information of step 323.

As a result, if the UE 310 determines in step 331 that it is in a radiochannel condition that is greater than a threshold Y and a size of themessage that the UE 310 will transmit over the uplink is greater thanthe minimum message size transmission-guaranteed even in the cellboundary, the UE 310 proceeds to step 332.

In step 332, the UE 310 randomly selects one random access preamble froma random access preamble set mapped to the above condition. However, ifthe condition of step 331 is not satisfied, the UE 310 randomly selectsone random access preamble from another random access preamble setseparately defined according to the present invention.

For example, under the assumption of the random access preamble designshown in Table 1, if, as given on the condition of step 331, the UE 310is in the radio channel condition that is greater than the threshold Yand the size of the message that it will transmit over an upper messageis greater than the minimum message size transmission-guaranteed even inthe cell boundary, the UE 310 randomly selects one of the random accesspreambles #0-#31 in the random access preamble set A.

However, if the condition of step 331 is not satisfied, the UE 310randomly selects one of the random access preambles #32-#63 in therandom access preamble set B.

In step 341, the UE 310 transmits the random access preamble selected instep 332 to the ENB 311. In step 342, the ENB 311 determines whichcondition the received random access preamble satisfies. That is, theENB 311 determines to which set the received random access preamblecorresponds, and based thereon, allocates radio resources for allowingthe UE 310 to transmit an upper message over the uplink, considering thestatus information (e.g., radio channel condition) of the UE 310.

For example, if the random access preamble received in step 341 is oneof the random access preambles #0-#31 in set A, the ENB 311 can allocatein step 342 radio resources for message transmission such that the UE310 can transmit a message, a size of which is greater than the minimummessage size transmission-guaranteed in the cell boundary.

However, if the random access preamble received in step 341 is one ofthe random access preambles #32-#63 in set B, the ENB 311 allocates instep 342 radio resources for message transmission such that the UE 310can transmit a message, a size of which equals to the minimum messagesize transmission-guaranteed in the cell boundary.

In step 343, the ENB 311 transmits to the UE 310 a response message tothe random access preamble received in step 341. The response messageincludes a random access preamble identifier indicating such informationas the received random access preamble, uplink timing sync informationfor matching uplink timing sync and radio resource information for thenext uplink upper message transmission.

The response message transmission of step 343 can be synchronized to therandom access preamble transmission of step 341 with a set timingrelationship. That is, if the UE 310 determines that the informationreceived in step 343 includes a random access preamble identifier mappedto the random access preamble transmitted in step 341 by the UE 310itself, the UE 310 corrects the uplink transmission timing using theuplink timing sync information included in the information received instep 343.

In step 351, the UE 310 transmits the corresponding upper message at thecorresponding channel/time using the radio resources allocated in step343. Here, the message transmitted in step 351 can be either an RRCmessage or a NAS message.

Alternatively, the message can be a combined message of the RRC messageand the NAS message. The RRC message indicates a message for RadioResource Control (RRC), having a UE and an ENB as protocol endpoints,and the NAS message indicates a message for controlling parameters suchas mobility, service and session of a UE, having a UE and an anchor nodeas protocol endpoints.

In addition, the ENB 311 can broadcast in step 323 an interference levelat an ENB antenna instead of the radio channel condition threshold Y.This can be defined as a third method.

Then, in step 331, if its maximum transmission power (Maximum UEtransmission power) is greater than or equal to a sum of the receivedinterference information at an ENB antenna (Interference at ENB), a pathloss measured in decibels [dB] calculated using transmission power andreception power for a downlink pilot channel, and an alpha, the UE 310determines that it is in a good radio channel condition. For this,reference can be made to Equation (3) below. Herein, the alpha can beeither fixed to one standard value, or transmitted in the systeminformation broadcasted in step 323.

However, in step 331, if the maximum transmission power of the UE 310 isless than or equal to the sum of the received interference informationat the ENB antenna, the path loss calculated using transmission powerand reception power for the downlink pilot channel, and the alpha, theUE 310 determines that it is not in the good radio channel condition. Inaddition, if the maximum transmission power of the UE 310 is greaterthan the sum of the received interference information at the ENBantenna, the path loss calculated using transmission power and receptionpower for the downlink pilot channel, and the alpha, the UE 310determines that it is in the good radio channel condition.

However, if the maximum transmission power of the UE 310 is less thanthe sum of the received interference information at the ENB antenna, thepath loss calculated using transmission power and reception power forthe downlink pilot channel, and the alpha, the UE 310 may determine thatit is not the good radio channel condition. In addition, if the maximumtransmission power of the UE 310 is greater than or equal to the sum ofthe received interference information at the ENB antenna, the path losscalculated using transmission power and reception power for the downlinkpilot channel, and the alpha, the UE 310 may determine that it is in thegood radio channel condition. In the aforementioned Equation (3),

1. Maximum UE Transmission Power≧Interference at ENB+Path_Loss+Alpha[dB]: UE is in good radio channel condition

2. Maximum UE Transmission Power≦Interference at ENB+Path_Loss+Alpha[dB]: UE is not in good radio channel condition  (3)

As described above, the UE 310 checks its own radio channel conditiondepending on the random access procedure-related parameters broadcastedin the cell, and separately selects a random access preamble from set Aor set B, which is a random access preamble selection condition,considering its own radio channel condition and the minimum sizenecessary for the next uplink upper message transmission.

The ENB 311 determines whether the random access preamble received fromthe UE 310 is transmitted from the separated set A or set B, therebyefficiently allocating radio resources.

FIG. 4 illustrates a UE's operation of selecting a random accesspreamble from a set separated based on the random access preamble designaccording to the present invention.

Referring to FIG. 4, if a random access procedure is triggered in step410, the UE checks in step 411 whether it is in a radio channelcondition that is greater than a threshold Y and a size of the messagethat the UE will transmit next is greater than the minimum message sizeZ transmission-guaranteed in the cell boundary. In step 411, the UE candetermine whether it is in a radio channel condition that is greaterthan a threshold in the method described in FIG. 3.

If the UE determines in step 421 that the condition of step 411 issatisfied, i.e. if the UE is in a radio channel condition that isgreater than the threshold and the size of the message that the UE willtransmit next is greater than the minimum message size Ztransmission-guaranteed in the cell boundary, the UE proceeds to step431.

In step 431, the UE selects a random access preamble set used when thecondition of step 411, guaranteeing the radio channel condition, issatisfied. For example, the UE will select the random access preambleset A of Table 1. However, if the UE determines that the condition ofstep 411 is not satisfied, the UE proceeds to step 432 where it selectsanother random access preamble set separated from the random accesspreamble set guaranteeing the radio channel condition. For example, theUE will select the random access preamble set B of Table 1.

In step 441, the UE randomly selects one random access preamble from therandom access preamble set separately selected in step 431 or 432.Thereafter, in step 451, the UE transmits the selected random accesspreamble to an ENB (or network node) over the uplink using thetime/frequency radio resources allocated for the random accessprocedure.

FIG. 5 illustrates an ENB's operation of allocating radio resourcesbased on the random access preamble design according to the presentinvention.

Referring to FIG. 5, in step 510, the ENB receives a random accesspreamble from a UE over a channel allocated for a random accessprocedure. In step 511, the ENB determines in which random accesspreamble set the random access preamble is included, by extracting thereceived random access preamble.

If it is determined that the random access preamble set determined instep 511 is included in the preamble set used when the UE is in a goodradio channel condition and a size of the message that the UE willtransmit next is greater than the minimum message sizetransmission-guaranteed in the cell boundary (‘YES’ in step 521), theENB proceeds to step 531.

In step 531, the ENB allocates radio resources so that the UE cantransmit a message, a size of which is greater than the minimum messagesize transmission-guaranteed in the cell boundary, for the message thatthe UE will transmit next.

However, if the ENB determines that the random access preamble setdetermined in step 511 corresponds to another preamble set separatedfrom the preamble set corresponding to the condition of step 521 (‘NO’in step 521), the ENB proceeds to step 532.

In step 532, the ENB allocates radio resources so that the UE cantransmit a message, a size of which is equal to the minimum message sizetransmission-guaranteed even in the cell boundary, for the message thatthe UE will transmit next.

In step 541, the ENB transmits, along with a response message to therandom access preamble, radio resource information for the message thatthe UE, allocated the radio resources in step 531 or 532, will transmitnext.

FIG. 6 illustrates a block diagram of a UE's apparatus for selecting arandom access preamble from a set separated based on the random accesspreamble design according to the present invention.

Referring to FIG. 6, the UE includes a radio channel conditiondeterminer 611, a message size determiner 612, a random access preambleset selector 621, a random access preamble selector 631 and atransceiver 641.

The radio channel condition determiner 611 determines whether the radiochannel condition of the UE is greater than a threshold Y. As describedin FIG. 3, the radio channel condition determiner 611 determines theradio channel condition depending on such information as CQI, a pathloss and an interference level at an ENB antenna.

The message size determiner 612 determines a size of the message thatthe UE will transmit next over the uplink. The message size determiner612 determines whether the message size is greater or less than theminimum message size transmission-guaranteed even in the cell boundary.

The random access preamble set selector 621 selects a random accesspreamble set that the UE will use, according to the decisions made bythe radio channel condition determiner 611 and the message sizedeterminer 612. The random access preamble set can be separated into oneset used when the radio channel condition is greater than the thresholdY and a size of the message that the UE will transmit next is greaterthan the minimum message size transmittable even in the cell boundary,and another set used when the above condition is not satisfied. That is,the random access preamble set selector 621 selects one of the set A andset B, which are random access preamble sets separated considering theprovided radio channel condition information and the message sizeinformation necessary for the next uplink upper message transmission.

For example, if the UE is in a radio channel condition that is greaterthan the threshold Y and a size of the message that the UE will transmitover an upper message is greater than the minimum message sizetransmission-guaranteed even in the cell boundary, the random accesspreamble set selector 621 selects the random access preamble set A.However, if the above condition is not satisfied, the random accesspreamble set selector 621 selects the random access preamble set Bseparated from the random access preamble set A.

The random access preamble selector 631 randomly selects one randomaccess preamble from the random access preamble set selected by therandom access preamble set selector 621.

The transceiver 641 transmits the random access preamble selected by therandom access preamble selector 631 to the ENB using the allocatedtime/frequency radio resource.

FIG. 7 illustrates a block diagram of an ENB's apparatus for allocatingradio resources based on the random access preamble design according tothe present invention.

Referring to FIG. 7, the ENB includes a transceiver 711, a random accesspreamble extractor 721, a random access preamble set determiner 731, ascheduler 741 and a random access preamble response message generator751.

The transceiver 711 receives a random access channel from a UE. Therandom access preamble extractor 721 extracts the random access preambletransmitted by the UE using the received random access channel.

The random access preamble set determiner 731 determines to which randomaccess preamble set the random access preamble parsed by the randomaccess preamble extractor 721 corresponds. The acquired random accesspreamble set result is delivered to the scheduler 741.

The scheduler 741 determines the radio channel condition of the UEdepending on the acquired random access preamble set. Therefore, thescheduler 741 determines radio resource allocation considering the radiochannel condition when allocating radio resources for the nexttransmission message of the UE.

The random access preamble response message generator 751 transmitsinformation on the radio resources allocated by the scheduler 741 to theUE via the transceiver 711, along with the random access preambleresponse message. If the random access preamble set determined by therandom access preamble set determiner 731 is the set used when the radiochannel condition of the UE is greater than the threshold Y and the sizeof the message that the UE will transmit next is greater than theminimum message size transmittable even in the cell boundary, thescheduler 741 allocates radio resources for a message, a size of whichis greater than the minimum message size, for the next transmissionmessage of the UE.

However, if it is determined that the random access preamble set checkedby the random access preamble set determiner 731 belongs to anotherrandom access preamble set that cannot satisfy the above condition, thescheduler 741 allocates radio resources corresponding to the minimummessage size for the next transmission message of the UE.

As is apparent from the foregoing description, the present inventionprovides a method and apparatus for allocating resources to guaranteethe message size transmittable by the UE considering the radio channelcondition of the UE in the next generation mobile communication system.

According to the present invention, the UE selects a random accesspreamble from the set separated considering the radio channel conditionand the message size. That is, the UE selects and transmits the randomaccess preamble guaranteeing the collision between UEs, therebyperforming the procedure for guaranteeing reliability between the UEperforming the random access procedure and the upper network node.

Further, according to the present invention, the network node allocatesradio resources fully considering the radio channel condition of the UE,thereby contributing to an increase in efficiency of the limited radioresources.

As a result, the present invention provides an efficient random accessprocedure in the mobile communication system, to allocate efficientradio resources for uplink transmission of the UE.

While the invention has been shown and described with reference to acertain preferred embodiment thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

What is claimed is:
 1. A method for performing a random access in awireless communication, comprising: identifying a channel condition anda size of a message that a user equipment will transmit after atransmission of a preamble; selecting a first preamble set from at leasttwo preamble sets if the channel condition is greater than a firstthreshold and the size of the message is greater than a secondthreshold; selecting a preamble from the selected first preamble set ifthe first preamble set is selected; transmitting, to a base station, theselected preamble; receiving, from the base station, a random accessresponse (RAR) message including resource allocation information inresponse to the transmission of the selected preamble; and transmitting,to the base station, the message based on the resource allocationinformation.
 2. The method of claim 1, further comprising: selecting asecond preamble set from the at least two preamble sets if the channelcondition is less than or equal to the first threshold or the size ofthe message is less than or equal to the second threshold; and selectinga preamble from the selected second preamble set if the second preambleset is selected.
 3. The method of claim 1, wherein the channel conditionis determined by comparing a transmission power to a reception power fora downlink pilot channel.
 4. The method of claim 1, wherein the firstthreshold is associated with a maximum transmission power and a value insystem information broadcasted by the base station.
 5. The method ofclaim 1, wherein the second threshold is configured by broadcastedsystem information.
 6. The method of claim 1, wherein the RAR messagefurther includes at least one of a preamble identifier mapped to thetransmitted selected preamble, uplink synchronization information, andresource information for a next uplink message transmission.
 7. Anapparatus for performing a random access in a wireless communication,comprising: a transceiver configured to transmit or receive data; and acontroller configured to: identify a channel condition and a size of amessage that a user equipment will transmit after a transmission of apreamble; select a first preamble set from at least two preamble sets ifthe channel condition is greater than a first threshold and the size ofthe message is greater than a second threshold; select a preamble fromthe selected first preamble set if the first preamble set is selected;transmit, to a base station, the selected preamble; receive, from thebase station, a random access response (RAR) message including resourceallocation information in response to the transmission of the selectedpreamble; and transmit, to the base station, the message based on theresource allocation information.
 8. The apparatus of claim 7, whereinthe controller is further configured to select a second preamble setfrom the at least two preamble sets if the channel condition is lessthan or equal to the first threshold or the size of the message is lessthan or equal to the second threshold, and to select a preamble from theselected second preamble set if the second preamble set is selected. 9.The apparatus of claim 7, wherein the channel condition is determined bycomparing a transmission power to a reception power for a downlink pilotchannel.
 10. The apparatus of claim 7, wherein the first threshold isassociated with a maximum transmission power and a value in systeminformation broadcasted by the base station.
 11. The apparatus of claim7, wherein the second threshold is configured by broadcasted systeminformation.
 12. The apparatus of claim 7, wherein the RAR messagefurther includes at least one of a preamble identifier mapped to thetransmitted selected preamble, uplink synchronization information, andresource information for a next uplink message transmission.